Background: Women with breast cancer are at increased risk of developing skin cancer. Little is known about how tamoxifen affects this risk. We aimed to investigate whether tamoxifen treatment following breast cancer is associated with skin cancer. Methods: A cohort consisting of 44,589 women diagnosed with breast cancer during 1977–2007 from the nationwide clinical database of the Danish Breast Cancer Cooperative Group, was followed for a primary skin cancer [basal cell carcinoma (BCC), squamous cell carcinoma (SCC) or melanoma] in the Danish Cancer Registry supplemented by data on BCC and SCC from the Danish Pathology Register. We investigated incidence of skin cancer among 16,214 women treated with tamoxifen compared to 28,375 women not treated with tamoxifen by calculating incidence rate ratios (IRRs) in Cox regression models. Results: Tamoxifen users were followed for a median of 2.9 years. The median duration of tamoxifen treatment increased from around 1 year among women diagnosed before 1999 to nearly 2.5 years among women diagnosed in 1999 or later. Women treated with tamoxifen had an IRR 1.06 (95 % CI 0.72–1.55) for SCC and an IRR 1.40 (95 % CI 0.95–2.08) for melanoma when compared to non-users. The observed number of these types of cancer (37 SCCs and 38 melanomas among users) did not allow stratification on calendar-period. The overall IRR for BCC was 0.96 (95 % CI 0.84–1.09), but the IRR differed by menopausal status and calendar-period at diagnosis of breast cancer. Conclusions: Our overall results indicate that tamoxifen is not associated with skin cancer. However, the inconsistency of results from stratifications prevents a firm conclusion.